1. Field of the Invention
The present invention relates to a lens driving device which is capable of applying an offset force to a spring component for suspending a lens support on a box body.
2. Description of Related Art
FIG. 11 is a section view illustrating an example of an existing voice coil motor type lens driving device 50. The lens driving device 50 suspends the lens support 52 which is used for keeping the lens 51 on a box body 53 by utilizing a spring component 56. The spring component 56 is composed of a front side spring component 56 A and a back side spring component 56B with approximately same structure. Moreover, a coil 54 for driving the lens is winded around a Z axis which acts as the optical axis of the lens 51. The coil 54 is installed on the lens support 52. And the magnet 55 for driving the lens is installed inside the box body 53 and is configured to be cylindrical so that the magnet 55 is magnetized in radial directions of the lens support 52. Under the condition that the coil 54 for driving the lens is electrified, the coil 54 for driving the lens generates a Lorentz force in a direction towards the object to be shot (hereinafter, also called in front of the Z axis, in the +Z direction or on the +Z side). The +Z direction is shown as an arrow labeled “Z” in FIG. 11, so that the lens support 52 moves to a position where a restoring force of the spring component 56 is balanced by the Lorentz force generated by the coil 53, and thus the lens 51 can move to a preset position.
Therefore, the box body 53 is provided with a disc-shaped base plate 53a of which an opening part 53h forms in the central part; a cylindrical side wall 53b, which is set up on the outer edge part of the base plate from the +Z direction; and a circular ring-shaped restricting part 53c, which is projected out from the inner edge part of the opening part 53h, and extends towards the lens support 52, and the position of the lens support 52 is restricted at the backmost position when the coil 54 for driving the lens is not electrified. Moreover, a magnet yoke 57 in the same figure shown as two L-shaped components in the section view is used for effectively guiding a magnetic field from the magnet 55 for driving the lens to the coil 54 for driving, a cylinder part 57a as a vertical sheet is configured between the magnet 55 and the side wall 53b of the box body, and a circular ring part 57b as a horizontal sheet is configured on the +Z side of the magnet 55 (for example, referring to patent literature 1: JP patent application 2007-171764).
FIG. 12A and FIG. 12B are diagrams illustrating a structural example of the existing spring component 56. The spring component 56 is provided with a circular ring-shaped inner side retaining part 56a installed on the lens support 52, an outer side retaining part 56b installed on the box body, a plurality of wrist parts 56c configured between the inner side retaining part 56a and the outer side retaining part 56b, a plurality of inner side connecting parts 56m each for connecting the inner side retaining part 56a with its one end and connecting an end of a corresponding one of the plurality of wrist parts 56c with its other end, and a plurality of outer side connecting parts 56n each for connecting the outer side retaining part 56b with its one end and connecting the other end of a corresponding one of the plurality of wrist parts 56c. When the spring component 56 is observed from the side of the object to be shot (in the +Z direction), each wrist part 56c is extended in the circumferential anti-clockwise direction (or clockwise direction) from the inner side retaining part 56a via a corresponding inner side connecting part 56m, and is connected with the outer side retaining part 56b through a corresponding outer side connecting part 56n. The wrist parts 56c are configured for playing a role of a spring in suspending the lens support 52 on the box body.
However, the lens driving device 50 is assembled by utilizing the following method. Namely, as shown in FIG. 13A, after the inner side retaining part 56a of the back side spring component 56B is fixedly connected (connected and fixed) to the end of the lens support 52 on the −Z side, the outer side retaining part 56b of the back side spring component 56B is pressed on the surface of the base plate 53a of the box body on the +Z side by utilizing clamps and so on, then an offset force is applied to the outer side retaining part 56b, and meanwhile the outer side retaining part 56b is fixedly connected onto the box body 53.
Then, as shown in FIG. 13B, the outer side retaining part 56b of the back side spring component 56B is wrapped from the +Z side by using a spacer 58, and after the magnet yoke 57 and the magnet 55 for driving the lens are overlapped on the spacer 58, the inner side retaining pat 56a of the front side spring component 56A is fixedly connected onto the end of the lens support 52 on the +Z side.
Finally, as shown in FIG. 13C, the outer side retaining part 56b of the front side spring component 56A is pressed on one surface of the circular ring part 57b of the magnet yoke 57 on the +Z side by using unshown clamps, and an offset force is applied to the outer side retaining part 56b, meanwhile the outer side retaining part 56b is fixedly connected with the box body 53.
In the assembling method as mentioned above, for the inner side retaining part 56a and the outer side retaining part 56b: after the inner side retaining part 56a of the spring component 56 is fixedly connected onto the lens support 52 and the inner side retaining part 56a and the lens support 52 are coplanar in a manner that the offset force is not applied, the outer side retaining part 56b is fixedly connected with the box body 53 or the magnet yoke 57 in a state that the offset force is applied to the outer side retaining part 56b towards the −Z side.
Therefore, the lens support 52 receives an acting force in the −Z direction opposite to the +Z direction all the time under the effect of the restoring force of the spring component 56, thus the lens support 52 can also be stably retained at the backmost position even if the optical axis of the lens driving device 50 is inclined relative to the plumb line direction.
However, as indicated by the hollow arrow G51 shown in FIG. 12A, if the spring component 56 is the front side spring component 56A, a pressing force is applied to the inner side retaining part 56a from the +Z direction to the −Z direction, and if the spring component 56 is the back side spring component 56B, a pressing force is applied to the inner side retaining part 56a from the −Z direction to the +Z direction, but both the front side spring component 56A and the back side spring component 56B need to be installed on the lens support 52. Therefore, when the inner side retaining part 56a of the spring component 56 is fixedly connected onto the lens support 52, the pressing force must be applied to the inner side retaining part 56a in a narrow range except the roots of the plurality of inner side connecting parts 56m. The reason is that, if the pressing force is applied to the roots of the inner side connecting parts 56m, the inner side connecting parts 56m will be greatly twisted or bent.
However, as shown in FIG. 12B schematically, even if the pressing force is prevented to be applied to the roots of the inner side connecting part 56m, the inner side connecting parts 56m cannot be prevented from being twisted or bent effectively, and the arc part except the root of the inner side retaining part 56a is bent and deformed in direction of X-Y plane, thus the outer side retaining part 56b rotates as shown in the arrow R, and a state of being inclined relative to the inner side retaining part 56a is formed. Therefore, the inner side retaining part 56a takes the Z axis direction as the normal direction, on the other hand, the outer side retaining part 56b is formed into the state of being rotated from the Z axis direction which causes incline, namely, the outer side retaining part 56b takes the Zr axis direction which is twisted from the Z axis direction as the normal direction.
Moreover, as indicated by the thick and black arrow G52 shown in FIG. 12A, when the offset force towards the side of the box body 53 is applied to the outer side retaining part 56b and the outer side retaining part 56b is connected with the box body 53, the restoring force in the +Z direction is generated for the wrist parts 56c since the offset force is applied, which results in the outer side connecting part 56n floating towards the +Z side, thus the outer side retaining part 56b needs to be pressed, and the pressing part is the circular ring part except the part connected with the root of the outer side connecting part 56n, and the pressing part is fixedly connected. Therefore, the circular ring part of the outer side retaining part 56 is badly bended near the root of the outer side connecting part 56n, and the outer side connecting part 56n is twisted, and the twisting of the outer side retaining part 56b relative to the Z axis direction is greater as mentioned above.
Hereon, the FIGS. 14A and 14B are used for detailedly describing the reason that the inner side retaining part 56a or the outer side retaining part 56b is bent and deformed in the directions of the X and Y plane when the inner side retaining part 56a or the outer side retaining part 56b is pressed.
As shown in FIG. 14A, the back side spring component 56B is configured at the back of the end of the lens support 52 in the −Z direction, for example, under the condition that the pressing force towards the +Z direction is applied to the inner side retaining part 56a of the back side spring component 56B and the inner side retaining part 56a is fixedly connected onto the lens support 52, the pressing force towards the +Z direction as show in the arrow G51 is applied to the inner side retaining part 56a on the −Z side by a plurality of inner side pressing clamps J51.
The lens support 52 and the box body 53 are respectively made from resin materials such as liquid crystal polymer or nylon, and there are soft and fine concave and convex points on the surfaces of these materials. Moreover, the thickness of the spring component 56 is formed to be about several 10 s-100 microns (in other words, about 10 microns to 999 microns), and the spring component 56 is easily deformed. Relatively, the inner side pressing clamp J51 is a clamp made of hard base material such as rolled steel so as to maintain the durability. Therefore, the spring component 56 arranged between the soft lens support 52 or the box body 53 and the hard inner side pressing clamps J51 is deformed under micro loading effect of the inner side pressing clamps J51.
Therefore, as shown in FIG. 14B, when the inner side retaining part 56a receives the pressing force of the inner side pressing clamps J51 so as to cling to the end of the lens support 52 on the −Z side, the inner side retaining part 56a is deformed along with the shape of the concave-convex on the surface of the lens support 52, and is sunken with the lens support 52 under the effect of the inner side pressing clamps J51, or is bent along the X direction and Y direction. As a result, the inner side connecting part 56m connected with the inner side retaining part 56a is twisted, while the wrist parts 56c are inclined and are bent and deformed along the X and Y directions.
Moreover, under the condition that the outer side retaining part 56b is connected to one surface of the base plate 53a of the box body 53 on the +Z side, the offset force is applied to the outer side retaining part 56b towards the −Z direction and meanwhile the outer side retaining part 56a is connected, thus the writ parts 56c generate the restoring force in the +Z direction, and the outer side retaining part 56b easily floats together with the outer side retaining part 56n. Therefore, as shown in FIG. 14C, the outer side retaining part 56b needs to be pressed in an extremely great range, but the root of the outer side connecting part 56n is deformed along the concave-convex shape of the box body 53, and the stress is concentrated on the edge part of the outer side pressing clamp J52, thus the part near the root of the outer side connecting part 56n is greatly deformed, or the outer side connecting part 56n is twisted, as a result that the twisting of the outer side retaining part 56b is greater relative to the inner side retaining part 56a. Moreover, under the conditions that the inner side retaining part 56a of the front side spring component 56A is connected to the end of the lens support 52 on the +Z side and the outer side retaining part 56b is connected to the surface of the magnet yoke 57 on the +Z side, the problems the same as that under the condition of the fixedly connected back side spring component 56B also appear.
As mentioned above, the spring component 56 is directly assembled on the lens driving device 50, the outer side retaining part 56b is twisted and inclined relative to the inner side retaining part 56a, and under the condition that the coil 54 for driving the lens of the lens driving device 50 is electrified, the lens support 52 forms the state of being slightly inclined relative to the original Z axis, the optical axis of the lens 51 is inclined, thus, when the lens support 52 begins to move towards the front of the Z axis (in the +Z direction), the problem that the lens driving device 50 is inclined appears.